Enhanced thermoelectric performance of Cu1.8S via lattice softening

Digenite received extensive attention in recent years owing to the good electrical and thermal stability as well as the characteristics of the environmental benignity and low cost. The major task of Cu1.8S material is to further optimize the thermoelectric performance by means of the Seebeck coefficient improvement and thermal conductivity reduction. In this study, the Cu1.8S based bulk material with the extraordinary high thermoelectric performance was obtained through alloying with AgCl, in which the Seebeck coefficient has been improved by carefully regulating the excessive hole carrier concentration. Besides, the FESEM, EDS and XPS results reveal that multiple phonon scattering centers have been introduced, and the liquid-like Ag+/Cu+ ions result in the chemical lattice softening and thus the weakened sound velocity. These advantageous factors cause the drastically decreased thermal conductivity as well as the remarkably optimized thermoelectric properties in Cu1.8S specimen with 1 wt% AgCl, achieving a record zT value of 1.5 at 773 K, among the currently optimum performance in Cu1.8S system materials.